The need for a self-help device which makes it possible to operate a vehicle with a flat or damaged tire without the need to change that tire is self-evident. Flat tires are a common occurrence. Even under the best of circumstances, their replacement is a cumbersome and dirty job. When the flat tire must be changed under conditions of darkness, in rain or snow, on the narrow shoulder of an express highway, on sloping terrain, or under any one of a number of other adverse conditions, the job becomes extremely unpleasant and frequently even dangerous.
It is also a fact that many cars are driven by women, in some cases elderly women, who find the mere mechanical task of changing a tire quite beyond their capacities. Women are also reluctant to engage in this particular task because it graphically displays their momentary helplessness to every passing motorist. In remote locations, and particularly at night, this represents a particular danger.
The need for such a device is particularly critical when the tire must be replaced in the middle of a busy lane for lack of shoulders on the road or impossibility of moving the car without ruining the flat tire. In such instances, heavy traffic flow may be completely stalled for a long period of time while the damaged wheel is changed, causing not only great inconvenience, but also air pollution and wastage of fuel.
To meet this need, many proposals have been made to provide a wheeled dolly or other support device onto which the flat tire can be driven, and which then enables the motorist to drive the vehicle to the nearest auto service station.
Support devices of this type normally have two rear wheels and one or two front wheels, the single front wheel usually being a caster wheel. The wheels are attached to a horizontal frame which contains a cradle in which the disabled tire can rest securely. In addition, the rear portion of the support device normally has a ramp which is pivotable from a first position in which it contacts the ground to a second, raised position to which it is pivoted by the wheel being mounted on the support member.
Support devices of the foregoing type are shown, e.g., in U.S. Pat. No. 2,350,118 (Knapp) and U.S. Pat. No. 3,145,860 (Graves). However, these prior art devices (and others mentioned hereinbelow) have a number of serious disadvantages which applicant has been able to overcome.
The Knapp patent discloses a three-wheeled truck comprising a single front caster wheel and a longitudinally extending strip which serves as a cradle for the wheel to be mounted. However, for the purpose of holding the truck stationary under the forward pressure of an entering wheel, the patentee mounts two stay pins for pivotal movement on the rear wheel axle. Each stay pin has a radius greater than that of the rear wheels, and engages the ground with a sharp knife edge, so that the wheels are elevated off the ground while the truck is in wheel receiving position. As the wheel is driven onto the ramp, the stay pins are driven into the ground by the weight of the wheel, thereby preventing the truck from moving forward. As the wheel moves forward towards the cradle, the rear wheel axle moves forwardly of the fixed fulcrum of the stay pins, causing these to swing rearwardly into dragging position, and the rear wheels drop to truck supporting position in contact with the ground. Detents integral with the ramp engage with lugs projecting from the stay pins to assure that pivoting of the ramp does not occur until the damaged tire has passed the axle of the rear wheels.
It will be clear from the foregoing discussion that, while Knapp indeed assures that the truck does not move forward during loading, he achieves this objective by extremely cumbersome means. The provision of stay pins with knife edges makes the truck heavy and unwieldy, and it is questionable how well the pins could "dig" into, e.g., the concrete pavement of a highway, or to what extent they would damage a non-concrete pavement, such as asphalt. Moreover, the stay pins would have to be extremely sturdy in order to withstand the considerable stress to which they are subjected during their movement from their forward, dug-in position to their rearward, dragging position. Another disadvantage resides in the fact that, for the entire subsequent travel of the vehicle, the pins would presumably drag along the pavement, causing both drag on the vehicle and damage to the pins themselves and to the pavement.
The Graves patent discloses a truck having a two-part ramp movable from an inclined position to a horizontal position. The device is rather complex. In the first place, it is only partly collapsible, by folding the rear ramp portion over the front ramp portion. Since each of these portions is also provided with integral half tube supports, the truck in its collapsed position can be regarded as compact only in terms of its limited size, which appears to limit its stability and carrying capacity correspondingly.
To keep the truck from rolling while the ramp is receiving the tire, Graves provides a plunger mechanism for locking the truck wheels in place. As the tire reaches the end of the ramp, the latter pivots to its horizontal position, causing it to press down on the plunger mechanism, thereby releasing the wheels. This arrangement is complicated and hence uneconomical, by contrast with the present invention which achieves the same result while using an extremely simple, rationalized structure.
While the Knapp patent does not provide any means of securing the tire once mounted, Graves does so by complicated means which will be compared hereinbelow with the simple mechanism conceived by applicant.